What is git? Git is version control. Additionally: I Content tracker I Collaboration tool I Notekeeping system I (Backup - if used correctly) This session: I Git I Concepts I Set up a repository I Add (“track”) files I Change files I Branches I Merging I GitHub I Set up a repository I Push, pull caveat emptor Git is both very simple and very complicated. But it is only as complicated as you need it to be. Distinction: Git vs GitHub Git The core software which actually creates and maintains repositories Fundamentally a command line tool with a very rudimentary GUI. Lots and lots of third party graphical interfaces. I Suggested: SmartGit, GitHub Desktop, RStudio I Others: TortoiseGit, Tower, SourceTree, GitKraken I List: https://git-scm.com/downloads/guis/ NB: Many of the GUIs simplify interacting with GitHub Distinction: Git vs GitHub GitHub An online service to store your repositories, collaborate with others and various other ‘value added’ services. Needs an account to use. Alternatives: BitBucket, GitLab, self-hosted It is perfectly possible and reasonable to use Git without using GitHub I But for simplicity. use GitHub. I NB: GitHub operates a student programme where ‘premium’ features and extras available for students for free for a year or so. Git basics I Fundamentally, git creates and stores snapshots of files and folders. I Git must be told to track files as you add them. I Adding new files is a two step process, involving (1) staging and (2) committing. Git basics 2 I When you delete a file, git notes it this: you will no longer see it in your folders. But previous versions of the file live in gits repository. I Everything is stored in the .git folder - normally hidden in Explorer/Finder. Aside: hidden files I Mac: Cmd+Shift+Dot to view hidden files I Windows: 1. Open File Explorer from the taskbar. 2. Select View > Options > Change folder and search options. 3. Select the View tab and, in Advanced settings, select Show hidden files, folders, and drives and OK. Some concepts Git ‘thinks’ in terms of 3 ‘trees’ (fancy word for directory structures) I working directory : what you see when you open Explorer/Finder and look at your project folder. I index : a.k.a staging area - an ‘intermediate’ area where changes are stored before committing. I HEAD : this points to the last/current commit*. All comparisons related to files - e.g. whether a file exists, deleted, changed - are done between these three trees. Unless you actively make it git will never permanently delete anything which has been committed (great safety feature!) Chacon S. Pro Git. Second edition. New York, NY: Apress; 2014. 426 p. URL: https://git-scm.com/book/en/v2 Some terminology I stage : add new files, or changes to already tracked files, to the staging area (aka index) - an intermediate step. I commit : I verb: add new files/changes to the history - create a ‘snapshot’. I noun: a previous ‘snapshot’ in history. NB: add and stage are interchangeable. stage more common in GUIs. [Walkthrough 1] My First Commit: Initialising a repository and adding a file [Walkthrough 2] Be The Change You Want To Be: Making Changes and Storing Them The commit history I The commit history is a list of all the commits, in order, of a given branch. I Command: git log I But most GUIs will show you a tree visually, which is easier to follow. Undoing changes - git revert, git reset I The key benefit of version control is the ability to undo changes - rollback in time. I But this requires more thought than at first glance. ! Git Revert Doesn’t Do What You Think ! I When you git revert you don’t go backwards. Instead, you go forwards by making an inverse commit to where you want to go. I Consider this in terms of snapshots and keeping all the snapshots. Going backwards means losing snapshots. I Going forwards making an inverse commit keeps the intermediate snapshots. I Often a source of confusion. git revert Consider: Commit A: Files +a, +b, +c ====> Result: Files a, b, c Commit B: Files +d, +e, changes a' ====> Result: Files a', b, c, d, e [revert!] Commit C: Files -a', -d, -e ====> Result: Files a, b, c If you ever need to, you can revert to commit B. Files d and e are in the history as well Reset I git reset : this resets the working directory OR index back to their last state. I This is probably what you want most of the time - used to undo changes/adding files into the index. I git restore filename : this will restore the last committed version of the file into the working directory. [Walkthrough 3] Back to the Future Git Branches I A branch is a parallel workstream. I Think of having a multiple working directories, each having independent work done on it. I Useful for: I Collaboration - so multiple people can work on aspects of a project without messing with the ‘master’ copy. I Testing - quickly test a new bit of code/work, pause it, return to master, carry on, go back to new code etc. Jens Lechtenbörger https://oer.gitlab.io/oer-on-oer- infrastructure/Git-introduction.html#/sec-title-slide Jens Lechtenbörger https://oer.gitlab.io/oer-on-oer- infrastructure/Git-introduction.html#/sec-title-slide Git branching commands I git branch branchname - create a new branch called branchname I git checkout branchname - switch to branchname I New versions of git: also use git switch branchname I git checkout -b branchname - shorthand for “create new branch branchname then switch to it”. [Walkthrough 4] Remotes! i.e. GitHub Git can store repositories in so called ‘remotes’. I A remote is just another location containing a copy of the .git folder. I Can be another folder on your computer, a network drive, service such as GitHub. I But your local copy must be told where the remote is. I This is a bit confusing how to do, I think. I Recommend: create the empty repository remotely (on GitHub) first. THEN clone the empty repository to your computer. That was the “remote” related information is already set up. NB You need to have a GitHub account Pull I Bring in any changes in the remote repository and merge them into the local one. I Commands: I git pull I The very first time you want to copy a remote repository: git clone Push I Send your committed changes up into the remote repository I Commands: I git push [Walkthrough 5] Tug o’ War Merging I Two common scenarios: I You’ve made some changes in Branch-B, but would like to merge them back in to Branch-A. I You’ve been working on your working directory and made some commits. However, meanwhile, Person-B else has committed some other changes to the repository on GitHub. You need to merge your and Person-B’s changes. Merging 2 I git merge operates on commits NOT individual files - endless source of frustration for me. I Merging happens from the POV of the receiving (destination) branch/commit. I All the changes from the source are brought into the destination. Jens Lechtenbörger https://oer.gitlab.io/oer-on-oer- infrastructure/Git-introduction.html#/sec-title-slide [Walkthrough 6] Merging lanes Wrap up I Use Git I Learning curve but will repay itself many times over. I Good research practice - keeping records. Other useful topics I Rebase - changing history I Bisect - made a mistake, now find the bug? I Git hooks - before every commit, do X. Or before push/pull, do Y etc I Worktrees - multiple branches of same repository in different folders I Cherry-pick - did a thing in branchB, want it in branchA but only that very specific thing, not all the history of branchB Other Resources I Git: I https://git-scm.org/ [NB GitHub Desktop will install Git itself on your computer] I Tutorials: I http://learngitbranching.js.org - highly recommended, not just about branching I https://rogerdudler.github.io/git-guide/ - a simple introduction I https://www.atlassian.com/git/tutorials - a series of fairly detailed (but comprehensive) tutorials I https://git-rebase.io/ - how to change history with git rebase I https://github.com/jlord/git-it-electron - Git-it app to teach you git I https://try.github.io/ - various things from GitHub I https://marklodato.github.io/visual-git-guide/index-en.html - A visual git reference I https://gitimmersion.com/ - another tutorial, needs a Ruby interpreter installed Other Resources I Reference/Resources: I https://git-scm.com/docs - Git Reference Manual I https://git-scm.com/book/en/v2 - Git Reference Book I https://www.atlassian.com/git/tutorials/atlassian-git- cheatsheet - Quick reference I Deep dive: I https://wyag.thb.lt/ - Write Yourself A Git [rewrite the entire core git program from scratch] I https://hackernoon.com/https-medium-com-zspajich- understanding-git-data-model-95eb16cc99f5 - an easy to read but very useful set of articles on git internals. I https://www.sbf5.com/~cduan/technical/git/ - Conceptual understanding Other Resources I Other VCS: SVN, Mercurial, Pijul, Fossil, DARCS, Bazaar I SUGAR - these are like ‘simplified’ wrappers on top of Git: I https://gitless.com I https://frostming.github.io/legit/ I Misc: I https://keepachangelog.com/en/1.0.0/ - discretizing your work and good commit messages I https://www.conventionalcommits.org/en/v1.0.0/ - a framework for good commit messages.